Max Waterman wrote:
Mark Hahn wrote:
I've written a fairly
simple bandwidth-reporting tool:
http://www.sharcnet.ca/~hahn/iorate.c
it prints incremental bandwidth, which I find helpful because it shows
recording zones, like this slightly odd Samsung:
http://www.sharcnet.ca/~hahn/sp0812c.png
Using iorate.c, I guess somewhat different numbers for the 2.6.15
kernel than
for the 2.6.8 kernel - the 2.6.15 kernel starts off at 105MB/s and
head down
to 94MB/s, while 2.6.8 starts at 140MB/s and heads town to 128MB/s.
That seems like a significant difference to me?
What to do?
Max.
Keep in mind that disk performance is very dependent on exactly what
your IO pattern looks like and which part of the disk you are reading.
For example, you should be able to consistently max out the bus if you
write a relatively small (say 8MB) block of data to a disk and then
(avoiding the buffer cache) do direct IO reads to read it back. This
test is useful for figuring out if we have introduced any IO performance
bumps as all of the data read should come directly from the disk cache
and not require any head movement, platter reads, etc. You can repeat
this test for each of the independent drives in your system.
It is also important to keep in mind that different parts of your disk
platter have different maximum throughput rates. For example, reading
from the outer sectors on a platter will give you a significantly
different profile than reading from the inner sectors on a platter.
We have some tests that we use to measure raw disk performance that try
to get through these hurdles to measure performance in a consistent and
reproducible way...
ric
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